A complementary MOS (CMOS) device comprises two types of MOS devices that are complementary to each other, i.e., p-type MOS (PMOS) device and n-type MOS (NMOS) device. Since one of the MOS device pair is always off, a CMOS device consumes power only during switching between on and off states. Thereby, the CMOS devices have been widely used in semiconductor devices. Typically, in a semiconductor device, CMOS devices are used in both the high voltage areas and the low voltage areas. For the operation under the different levels of voltages, the CMOS devices and the related elements may have different modified structures. The CMOS devices used in the high voltage areas are also known as high-voltage CMOS (HV CMOS) devices. The CMOS devices used in the low voltage areas are also known as low-voltage CMOS (LV CMOS) devices.